Earlier this week, we noted that Iran had reportedly sent “thousands” of troops to Syria in preparation for an offensive aimed at retaking the city of Aleppo.

With a population of more than 2 million, Aleppo was Syria’s largest city prior to the war and it’s now run by a hodgepodge of rebels and militants including al-Qaeda, the Free Syrian Army, and ISIS.

To get an idea of the effect the war has had on the city, have a look at the following before and after nighttime light emissions images:

The battle is also notable for the scale of Iran’s involvement. Between Hezbollah and Iranian forces, the battle for Aleppo is shaping up to be the largest ground operation orchestrated by Tehran to date.

Syrian troops backed by Hezbollah and Iranian fighters launched an offensive south of Aleppo on Friday, expanding their counter-attack against rebels across western Syria with support from Russian air strikes.

Aleppo, a commercial and industrial hub near the border with Turkey, was Syria’s largest city before its four-year civil war, which grew out of protests against Assad’s rule.

Control of the city, still home to two million people, is divided between the government and rebels.

“This is the promised battle,” a senior government military source said of the offensive backed by hundreds of Hezbollah and Iranian forces which he said had made some gains on the ground.

It was the first time Iranian fighters had taken part on such a scale in the Syrian conflict, he said, although their numbers were modest compared to the army force. “The main core is the Syrian army,” the source said.

Hezbollah, which has supported Assad in several battles during the civil war, said the army was carrying out a “broad military operation” with support from Russian and Syrian jets. It made no mention of Hezbollah fighters in its brief statement.

Two senior regional sources told Reuters this week that Iran has sent thousands of troops to Syria to bolster an offensive underway in Hama province and ahead of the Aleppo attack.

Russian air cover is backing offensives by Syria’s army and allied militias in the central provinces of Homs and Hama, as well as Aleppo in the north and Latakia along the coast.

On Friday, the Syrian army pushed south from the provincial capital Aleppo city, where control is divided between regime and rebels forces, as Russian air strikes pounded the villages of Al-Hader and Khan Tuman and nearby localities.

“The Syrian army started a new front on Friday and advanced to take control of the villages of Abteen and Kaddar” about 15 kilometres (12 miles) south of Aleppo city, said Observatory head Rami Abdel Rahman.

He said “dozens” of Russian aerial attacks in the past 24 hours had struck the area, which is controlled by a patchwork of groups including rebels, Islamist fighters and Al-Qaeda’s Syria affiliate, Al-Nusra Front.

Note also that Aleppo is near the so-called “anti-ISIS” zone that the US and Turkey humorously proposed to create a few months back, which means that Iran, supported by Russian air power, is now conducting an all-out ground assault very near territory Turkey likes to think it effectively patrols (if not controls).

But the real key here, is this (again from Reuters): “The assault means the army is now pressing insurgents on several fronts near Syria’s main cities in the west, control of which would secure President Bashar al-Assad’s hold on power even if the east of the country is still held by Islamic State.”

In other words, if Iran and Russia manage to retake Aleppo (and you know they will because remember, thanks to Hezbollah, this isn’t a team that’s going to be confused by the vagaries of urban warfare), Assad’s rule is restored.

Just like that.

From there, the situation would morph and what you would have is a kind of Wild West scenario, only in Syria “West” would mean “East” and Assad, Russia, and Iran, having secured most of the critical cities and territory, would be free to simply mount up and push east on a kind of search and destroy mission.

So apparently, the US and its regional allies in Riyadh and Doha have a couple of weeks to figure out what to do here or else this is going to be over and suddenly, Washington will find itself in the awkward position of having to negotiate for a transition away from an Assad government that has been fully restored.